IDLE in general doesn't recognize and support control characters commonly used in terminals.  This is often a problem with running things that show a progress bars, which usually print "\r" to return the cursor to the beginning of the line and then overwrite the line, over and over again.  Since IDLE doesn't support this properly, what you get instead is all of the progress output one after another on a single line.

To make matters worse, very long lines make IDLE's shell increasingly slow, at worst becoming almost entirely unresponsive.  This compounds the issue with progress bars.

It would be interesting to see what Jupyter does in these cases, since apparently such examples work well in Jupyter.  Perhaps we can do something similar.